Using a Dptki/kiTgfbr2fl/fl PDAC GEMM, Krishnamurty et al. provided direct genetic evidence that DPT+ universal fibroblasts give rise to LRRC15+ CAFs in a TGFBR2-dependent manner during tumorigenesis, constituting a central fibroblast axis in multiple human cancers. Selective depletion of LRRC15+ CAFs reverted this stromal compartment to a universal fibroblast-like state and significantly delayed pancreatic tumor growth in CD8+ T cell-dependent manner. LRRC15+ CAF depletion enhanced intratumoural CD8+ T cell effector function and potentiated antitumor immunity in response to anti-PD-L1 checkpoint blockade.
Contributed by Shishir Pant
ABSTRACT: Recent single-cell studies of cancer in both mice and humans have identified the emergence of a myofibroblast population specifically marked by the highly restricted leucine-rich-repeat-containing protein 15 (LRRC15)1-3. However, the molecular signals that underlie the development of LRRC15+ cancer-associated fibroblasts (CAFs) and their direct impact on anti-tumour immunity are uncharacterized. Here in mouse models of pancreatic cancer, we provide in vivo genetic evidence that TGFβ receptor type 2 signalling in healthy dermatopontin+ universal fibroblasts is essential for the development of cancer-associated LRRC15+ myofibroblasts. This axis also predominantly drives fibroblast lineage diversity in human cancers. Using newly developed Lrrc15-diphtheria toxin receptor knock-in mice to selectively deplete LRRC15+ CAFs, we show that depletion of this population markedly reduces the total tumour fibroblast content. Moreover, the CAF composition is recalibrated towards universal fibroblasts. This relieves direct suppression of tumour-infiltrating CD8+ T cells to enhance their effector function and augments tumour regression in response to anti-PDL1 immune checkpoint blockade. Collectively, these findings demonstrate that TGFβ-dependent LRRC15+ CAFs dictate the tumour-fibroblast setpoint to promote tumour growth. These cells also directly suppress CD8+ T cell function and limit responsiveness to checkpoint blockade. Development of treatments that restore the homeostatic fibroblast setpoint by reducing the population of pro-disease LRRC15+ myofibroblasts may improve patient survival and response to immunotherapy.